1. Technical Field
The present invention relates to machine tools furnished with: a bed; a table on which a workpiece is carried and which is disposed on the bed; a main spindle for retaining a tool, and provided to rotate freely on its center axis; a feed mechanism for shifting the table and the main spindle relatively to each other along three orthogonal axes within the machining area, and a cover for covering the machining area.
2. Description of the Related Art
Such machine tools known to date include the example composed of, primarily: a bed made up of a rectangular base, two sidewalls provided standing along respective right and left sides of the base and opposing each other across an interval; a table on which a workpiece is carried and which is disposed on the base portion of the bed; a cross beam made from a long beam disposed lengthwise between the sides with the longitudinal end parts of the cross beam supported on top of the side walls of the bed so that the cross beam can move freely within a horizontal plane along the front-to-back orientation of the bed; a saddle that is supported to move freely horizontally side-to-side (right-to-left) on the front of the cross beam; a spindle head that is supported to move freely vertically on the front of the saddle; and a main spindle that holds a tool and is supported by the bottom end portion of the spindle head so that the axis of the main spindle is vertical and the main spindle can rotate freely on the main spindle axis above the table.
This machine tool also has a first feed mechanism for moving the cross beam back and forth, a second feed mechanism for moving the saddle side to side, a third feed mechanism for moving the spindle head vertically, a rotational drive mechanism for rotating the main spindle on the main spindle axis, and a cover that encloses the machine tool and has doors that open by sliding side-to-side at the front (the front of the bed).
A workpiece held on the table is processed by the tool held by the main spindle as a result of the first feed mechanism moving the cross beam back and forth, the second feed mechanism moving the saddle side-to-side, the third feed mechanism moving the spindle head vertically, and the rotational drive mechanism rotating the main spindle on the main spindle axis. Chips, swarf, and other waste produced during machining, and cutting fluid supplied as needed to the point of contact between the tool and the workpiece flies outside the machining area but is prevented from exiting the machine tool by the cover.
When the workpiece is relatively small and light, the operator can load and unload the workpieces from the table, but when the work is heavy and large a crane or other type of hoist must be used to place the workpiece in and remove the workpiece from the machine tool. In this situation, however, the doors of this cover may not afford an opening that is large enough to carry the workpiece in and out of the machine tool, thus requiring removing part of the cover. This prevents efficiently changing the workpiece on the table.
Japanese Unexamined Utility Model App. Pub. No. H06-24847 discloses a machine tool having a cover comprising a front cover, a first top cover, a second top cover, and a third top cover. The front cover has a door that slides side-to-side to open, and is disposed in front of the base portion of the bed to cover the space enclosed between the two side walls of the bed. The first top cover is disposed between the side walls on both sides of the bed and covers the top of the space between the side walls. The second top cover is disposed covering the top of this space between the left side of the spindle head, the left side wall of the bed, the front of the cross beam, and the first top cover. The third top cover is disposed covering the top of this space between the right side of the spindle head, the right side wall of the bed, the front of the cross beam, and the first top cover.
The first top cover is an extensible/retractable sheet that shifts back and forth and allows the spindle head (cross beam) to move back and forth. One end of the first top cover is connected to the top of the cover so that the first top cover can be freely disconnected, and the other end is connected to the front of the spindle head.
The second top cover and third top cover are also extensible/retractable sheets that can move side-to-side and allow the spindle head (saddle) to move side-to-side. One end of the second top cover is connected to the top of the left side wall of the bed, and the other end is connected to the left side of the spindle head. One end of the third top cover is connected to the top of the right side wall of the bed, and the other end is connected to the right side of the spindle head.
The other end part of the first top cover is connected to the spindle head so that the spindle head can move vertically and side-to-side, and the one end of the second and third top covers is connected to the left wall and right wall, respectively, of the bed so that the top covers can move back and forth with the cross beam.
When a crane or other hoist mechanism is used to carry workpiece into or remove workpiece from this machine tool having a front cover, first top cover, second top cover, and third top cover, the one end of the first top cover is disconnected from the front cover and rolled up toward the spindle head. Thus rolling up the first top cover and opening the door of the front cover efficiently forms the opening needed to move workpiece into and out from the machine tool, and therefore enables efficiently changing the workpiece.
A problem with the machine tool disclosed in Utility Model App. Pub. No. H6-24847, however, is that in order to roll the first top cover to the spindle head and open the part covered by the first top cover, the one end of the first top cover must be disconnected from the front cover and rolled toward the spindle head. After the workpiece is changed, the first top cover must then be unrolled and the one end reattached to the front cover. This is tedious and time-consuming.